/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 1985-2013, University of Amsterdam
			      VU University Amsterdam

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/

#ifndef PL_SEGSTACK_H_INCLUDED
#define PL_SEGSTACK_H_INCLUDED

#define SEGSTACK_CHUNKSIZE (1*1024)

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
The segchunk struct has its data attached   to  its back. The data field
itself is typed double to ensure that   the  data is properly aligned to
allow access of doubles. This is needed to get properly aligned pointers
after topsOfSegStack() in evalExpression().
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

typedef struct segchunk
{ char  *top;				/* top when closed */
  size_t size;				/* size of the chunk */
					/* below clean using memset() */
  int	 allocated;			/* must call free on it */
  struct segchunk *next;		/* double linked list */
  struct segchunk *previous;
  double data[1];			/* data on my back */
} segchunk;

#define CHUNK_DATA(c)	((char *)(c)->data)

typedef struct
{ size_t   unit_size;
					/* below clean using memset() */
  segchunk *first;
  segchunk *last;
  char	   *base;
  char	   *top;
  char	   *max;
} segstack;


static inline int
emptySegStack(segstack *s)
{ return (s->top == s->base) &&
	 (s->last == NULL || s->last->previous == NULL);
}


#define popSegStack(stack, to, type) \
	( ((stack)->top >= (stack)->base + sizeof(type))	\
		? ( (stack)->top -= sizeof(type),		\
		    *to = *(type*)(stack)->top,			\
		    TRUE					\
		  )						\
		: !(stack)->last || !(stack)->last->previous ? FALSE \
		: popSegStack_((stack), to)			\
	)

#define pushSegStack(stack, data, type) \
	( ((stack)->top + sizeof(type) <= (stack)->max)	\
		? ( *(type*)(stack)->top = data,		\
		    (stack)->top += sizeof(type),		\
		    TRUE					\
		  )						\
		: pushSegStack_((stack), &data)			\
	)

COMMON(int)	pushSegStack_(segstack *stack, void* data) WUNUSED;
COMMON(int)	pushRecordSegStack(segstack *stack, Record r) WUNUSED;
COMMON(int)	popSegStack_(segstack *stack, void *data);
COMMON(void*)	topOfSegStack(segstack *stack);
COMMON(void)	popTopOfSegStack_(segstack *stack);
COMMON(void)	scanSegStack(segstack *s, void (*func)(void *cell));
COMMON(void)	clearSegStack_(segstack *s);

		 /*******************************
		 *	       INLINE		*
		 *******************************/

static inline void
clearSegStack(segstack *s)
{ if ( s->first )
    clearSegStack_(s);
}


static inline void
topsOfSegStack(segstack *stack, int count, void **tops)
{ char *p = stack->top - stack->unit_size;
  char *base = stack->base;

  for(;;)
  { while(count > 0 && p >= base)
    { *tops++ = p;
      p -= stack->unit_size;
      count--;
    }

    if ( count > 0 )
    { segchunk *chunk = stack->last->previous;

      p = chunk->top - stack->unit_size;
      base = CHUNK_DATA(chunk);
    } else
      break;
  }
}


/* quickPopTopOfSegStack() only performs a pop if we do not
   need to discard a chunk.  $collect_findall_bag/2 needs
   addition synchronization in that case.
*/

static inline int
quickPopTopOfSegStack(segstack *stack)
{ if ( stack->top >= stack->base + stack->unit_size )
  { stack->top -= stack->unit_size;
    return TRUE;
  }

  return FALSE;
}


static inline void
popTopOfSegStack(segstack *stack)
{ if ( !quickPopTopOfSegStack(stack) )
    popTopOfSegStack_(stack);
}


static inline void
initSegStack(segstack *stack, size_t unit_size, size_t len, void *data)
{ stack->unit_size = unit_size;

  if ( len )
  { segchunk *chunk = data;

#if O_DEBUG
    assert(len > sizeof(*chunk));
    assert(unit_size%sizeof(void*) == 0);
#endif
    chunk->size = len;
    stack->base = stack->top = chunk->top = CHUNK_DATA(chunk);
    stack->last = stack->first = chunk;
    stack->max  = addPointer(chunk, len);
    memset(&chunk->allocated, 0,
	   offsetof(segchunk,data)-offsetof(segchunk,allocated));
  } else
  { memset(&stack->first, 0, sizeof(*stack)-offsetof(segstack,first));
  }
}

#endif /*PL_SEGSTACK_H_INCLUDED*/
